In general, the demand for secondary batteries has been rapidly increased as technology development and demand with respect to mobile devices have increased. Among these secondary batteries, lithium (ion/polymer) secondary batteries having high energy density and operating voltage as well as excellent shelf and cycle life characteristics have been widely used as energy sources of various electronic products as well as various mobile devices.
Referring to Korean Patent Application Laid-Open Publication No. 2008-0052869, a structure of a general secondary battery is disclosed, and more particularly, a structure of a pouch-type secondary battery having a symmetric and approximately rectangular shape is disclosed.
Typically, in terms of the use of the space of a device in which a secondary battery is installed, the above secondary battery having a rectangular shape is advantageous. However, in a particular case, the secondary battery having a rectangular shape rather constrains the use of the space of a device. For example, smart phones are designed with an ultra thin profile for the ease of portability, and there are many cases that the total thickness thereof is less than 1 cm. Since a secondary battery and various electronic components as well as a camera module must be all installed in a limited internal space of the smart phone, the arrangement of these components are very important. However, since the camera module is capable of zooming in and out and includes a plurality of lenses, it is very difficult to reduce the thickness thereof. Also, since a high-capacity secondary battery is used for a prolonged operation of the smart phone, it is also very difficult to reduce the thickness of the secondary battery. Therefore, the camera module and the secondary battery are not disposed by being overlapped with each other, but must be disposed by being spaced apart from each other in the internal space of the smart phone.
Since the shape of the secondary battery is limited as described above, the installation position of each component is inevitably limited to a particular position, particularly in a small electronic device. As a result, the size and design of the device is considerably limited.
As a structure capable of addressing the above limitations, a perforated-type secondary battery has been developed in which a hole is formed in the center thereof. Secondary batteries are broadly categorized as a jelly-roll type; a stack and folding type, and a stacked type according to the shape of an electrode assembly, and the jelly-roll type and stack and folding type electrode assemblies are not suitable for preparing the perforated-type secondary battery.
Thus, only the stacked type electrode assembly, which is formed by separately stacking electrodes and separators, may be used in the perforated-type secondary battery. However, with respect to the stacked type electrode assembly, an excessively long period of time may be required for a process of aligning each layer by matching each hole formed in the plurality of electrodes and separators which constitute the electrode assembly. Even in the case in which the electrodes and separators are stacked by matching each hole formed in the plurality of electrodes and separators, a case frequently occurs in which the separators are deformed during a process of pressurizing or heating the electrodes and separators to change the position and shape of the hole. As a result, the perforated-type secondary battery is only at the level of idea and has not been commercialized yet.